1. Field of the Invention
The present invention generally relates to material cutting mechanisms and, more particularly, to oscillatory blade power saws.
2. Description of the Prior Art
The cutting of materials is often required in the fabrication and repair of various structures. In structures which are subject to corrosion or rusting such as in plumbing and automotive applications, in particular, existing parts must often be cut away in order to make repairs. In these particular environments, clearances are often exceptionally close since ease of repair does not justify design of greater clearances in view of the relative infrequency with which such repairs will be required, often at intervals of several years or more. Often, in plumbing environments, installation will be guided solely by economy with little or no thought being accorded to ease of repair beyond the requirements of regulatory codes.
Cutting mechanisms have taken several forms in consideration of the problem of removal of the material for the cut itself. In some types of pipe cutters using a sharpened wheel which rides against the cylindrical section of pipe to be cut, the material is malleably deformed at the edge of the cut. This technique is generally successful even at high relative hardnesses of the material to be cut if the thickness through which the cut is made is small.
Heat has also often been used to cut materials by burning or melting of the material. However, the geometry and other properties of the resulting material will often be adversely affected. For instance, it will often be necessary for melted material to be removed from the material after cutting is completed. Also, either the heating required for the cutting or the technique such as grinding used to remove melted material or both may compromise protective coatings such as galvanizing.
Generally, saws have provided the best technique of cutting materials since saw blades are generally fabricated in a manner to provide for a kerf of the cut which provides ample clearance for the saw blade and also provides for the carrying of materials from the kerf. However, sawing of malleable metals often causes distortion of the material cut, such as deforming tubing out of round, making the joining to other fittings difficult.
A problem common to all of the above cutting techniques is the requirement of space around the object to be cut. For instance, wheel-type pipe cutters require space for the wheel to be carried around the entire periphery of a pipe as well as some mechanism for bearing against opposing surfaces of the pipe and applying pressure from the cutting wheel to the pipe. Cutting arrangements using heat require sufficient space to avoid application of damaging amounts of heat to adjacent structures and invariably present a fire hazard. Saws must be reciprocated and common, rigid, blades require a clearance equal to a convenient length of saw stroke, commonly equal to the cross-sectional dimension in the direction of the cut so that material cut from the saw kerf can be carried out of the kerf, avoiding filling of the saw blade interstices between the teeth thereof.
More recently, flexible "saw" blades have been developed which consist of a flexible wire which is coated with a relatively coarse abrasive such as tungsten carbide particles. Principal applications of such blades have been where transportation of the "blade" to the location of the cut has been difficult, such as with tree limbs where a rope can be used to carry the blade into position and to reciprocate the blade against the material to be cut. In this way, the blade can often be reciprocated against the work from a relatively remote location.
Such abrasive wires have also been used in metal-cutting "hacksaws" where the abrasive wire is stretched in a straight line across the frame of the saw body rather than freely wrapped about the periphery of a workpiece such as a tree limb. However, such applications of abrasive wires has not been fully successful since the abrasive wire, unlike a conventional saw blade, does not have a planar spine which helps to guide the direction of the blade in the cut. Further, the abrasive coated wire is generally thicker than the set of teeth (e.g. the bending of teeth to both sides of the saw blade so that the kerf is wider than the thickness of the blade to provide relief from binding of the blade and workpiece) on a conventional blade. Therefore, the abrasive wire makes a larger kerf and requires the removal of more material. While the abrasive wire cuts quickly because material is removed in both directions of the stroke, the amount of additional work incident to the removal of more material from the kerf as well as the difficulty of blade control, mentioned above, have outweighed the advantage of greater potential cutting speed.
In any event, the use of abrasive wires in other replaceable blade saw frames does not improve the convenience of using such saws in close quarters. On the contrary, so-called "close quarters hack saws are merely blade holders which do not provide for applying tension to the blade but, instead, rely on the stiffness of conventional hack saw blades.
All of the above material cutting arrangements described above have been of the manually operated type which is generally preferred or necessary when cutting must be done in close quarters with restricted clearances. Power saws are generally of either a stationary or portable type and stationary saws (e.g. table saws, band saws and the like) where the workpiece must be brought to the saw are simply not appropriate to work in close quarters. Portable saws are generally of the circular or reciprocating type.
Circular saws are characterized by circular blades which may be of different diameters to achieve desired tooth velocities or to accommodate different sizes of work. However, since the blade must be rotated from its center, it is not usually applicable to close quarters. Since the cutting depth is limited to the radius of the blade, the clearance for a cut where the blade reaches through the workpiece must be almost as large as the diameter of the blade. Even if a circular blade of small diameter could be passed around the periphery of a workpiece such as a pipe, the minimum clearance would be similar to that of wheel-type pipe cutters mentioned above and other difficult problems would arise such as guiding the blade and the provision of an angled drive at small size capable of transmitting sufficient power to efficiently cut materials such as metals.
Reciprocating power saws are known, as well, and are marginally better suited to work with small clearances. However, to avoid clogging of the teeth of the blade, reciprocating power saws must have a stroke which slightly exceeds the maximum depth of cut. Therefore, reciprocating power saws are usually designed with a stroke of at least one inch or greater so that a common material thickness of 3/4 inch can be efficiently cut without blade clogging. The blade stroke is fixed in the geometry of the saw and generally cannot be changed. Even if the stroke could be changed, the avoidance of blade clogging infers that the blade stroke must cause the blade to protrude from the rear of the workpiece by a distance equal to the thickness of the workpiece.
In summary, the geometrical constraints imposed by the operation or construction of saw blades has severely limited their applicability to work having close clearances, particularly for power saws. In applications having close clearances, there is often no alternative to manual saws which, even then, cannot be conveniently used, if usable at all. At the present state of the art, a minimum clearance of required for virtually any type of cutting tool. Further, the operation of any tool in close quarters causes an increased safety risk, particularly with power tools.